The dynamic properties of solids couple to atomic motion and the relevant time-scale is that of a vibrational period, which is approximately equal to 100 femtoseconds (0.0000000000001 seconds). This is the time scale on which molecular dynamics, chemical reactions and phase transitions in solids occur. In contrast with existing, femtosecond laser probes, X-rays have a wavelength approximately equal to the distances between atoms, and hence enable atomic movements to be visualised directly. Thus, the natural technique for studying evolving atomic structures is through X-ray diffraction. Since their discovery, X-rays have been the dominant tool for determining atomic structures. We believe that the availability of time-resolved structural probes with sub-picosecond time-resolution which employ X-ray diffraction, would enable groundbreaking work by allowing the interrogation of rapidly changing structures. Currently these activities are pursued in collaboration with research groups worldwide in order to utilise existing femtosecond X-ray sources.